CMake Wildcard for TARGET_OBJECTS

Question

I have the following directory structure

-  CMakeLists.txt
-  include
    -  a.hh
-  lib
    -  CMakeLists.txt
    -  a.cc
-  src
    -  CMakeLists.txt
    -  main.cc
-  test
    -  CMakeLists.txt
    -  test.cc

I am using CMake for compiling test.cc using the command

add_executable(test test.cc $<TARGET_OBJECTS:A>)

and the object file A.o is compiled as

add_library(A OBJECT A.cc)

but the $<TARGET_OBJECTS:A> command becomes ugly very quickly. Is there any way to tell CMake to include all .o files in the lib folder for linking everything?

I would say there is nothing like wildcards that isn't at least as long as the command you are currently using (and which would still be cross-platform compatible). Can you elaborate a little on what you mean with "getting ugly"? There is maybe a solution that hides if you are using object libraries in a macro, but I'm not sure if this is the direction you want to go. — Florian, Feb 29 '16 at 09:49
By getting ugly, I mean, the list of linked libraries grows long enough to be untrackable and hence error prone. Object A, Object B and so on, and may be you forgot C in list of 5 and you didn't notice. — , Feb 29 '16 at 09:54
You may collect all references to your static libraries in list variable, and use it for create executable: `set(my_source_libs)`, `list(APPEND my_source_libs $)`, `list(APPEND my_source_libs $)`, ...,`add_executable(test test.cc ${my_libs})`. There are many other *programming* ways to achive similar effect. — Tsyvarev, Feb 29 '16 at 10:39

score 3 · Accepted Answer · edited May 23 '17 at 12:24

Turning my comment into an answer

There is no build-in syntax like wildcards to simplify your add_executable(test test.cc $<TARGET_OBJECTS:A>) command.

Actually - to improve the convenience of handling object libraries in my current project - I've gone all the way of modifying my CMake version's source code to extend the target_link_libraries() to accept object libraries the same way it does static or shared libraries.

But there are other ways that may help you handling large amounts of object libraries:

You could group object libraries into intermediate static libraries (but that somehow negates the effect of using object libraries):
```
add_library(A OBJECT a.cc)
add_library(B OBJECT b.cc)
add_library(AB $<TARGET_OBJECTS:A> $<TARGET_OBJECTS:B>) 
```

You could "extend" the functionality of add_executable() e.g. with a function like:

function(my_add_executable _target)
    foreach(_source IN ITEMS ${ARGN})
        if (NOT TARGET "${_source}")
            list(APPEND _source_list "${_source}")
        else()
            get_target_property(_type "${_source}" TYPE)
            if (_type STREQUAL "OBJECT_LIBRARY")
                list(APPEND _source_list "$<TARGET_OBJECTS:${_source}>")
            else()
                message(SEND_ERROR "my_add_executable: '${_source}' given as parameter is not a object-library target.")
            endif()
        endif()
    endforeach()
    add_executable(${_target} ${_source_list})
endfunction(my_add_executable)

Then you could mix your source files with names of object libraries. To prevent to much confusion I would recommend using more descriptive object library names (e.g. by adding a "Objs" suffix):

add_library(AObjs OBJECT a.cc)
...
my_add_executable(testA test.cc AObjs)

References

CMake properties and expanding generator expressions

do you have any plans to upstream your code to cmake for your modified `target_link_libraries`, that would be immensely useful. — therealjumbo, Dec 14 '16 at 20:18
second option of appening target_objects to a list does not seem to work. Atleast for 3.17. Is there a better way ? By the way, I was creating a library rather than an executable. — user2914066, Jul 20 '20 at 16:40

CMake Wildcard for TARGET_OBJECTS

1 Answers1

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